Battery size and solar panel (s)

[EM4]

I have a 1989 Sun-lite popup camper...8ft. on a 2007 Tundra 2nd gen. All I have in the camper that draws from 1 deep cycle Bat rated at 109 amps, is a furnace, water pump and lights with led's. Also an inventer thats only used for charging phones ipads etc. I am good with mechanics but electrical is more complicated. Will a 50 watt solar panel be enough to keep the battery topped up or should I add another 50 watts. While driving my truck alternator charges my house battery....directly connected with a Solenoid to separate the house from the truck battery. Also I live in Las Vegas and mainly travel in Nevada and Arizona in the winter so lack of sun isn't an issue.

 

[Vic Harder]

Generally, a good working solar system uses 2x the PV panels as the AH of the battery bank. Meaning you would need 218 Watts of solar. That rule of thumb also assumes you will be drawing the batteries down every night, which might not be true in your case.

The furnace is going to use the most power in your setup (no fridge?) and those use about 5A, and will be on (given Nevada/Arizona travel plans) no more than 6 hours per night... as a guess. That's 30 AH.

A 50W panel is going to put out a rough max of 50/12 = 4 Amps or so, and charging happens about 8 hours a day, and at no more than 80% efficiency, because of dust, angle to the sun, etc. 8hrs*.8*4A = 25AH BEST CASE.

Thus, you need more solar panel, for sure. I would look at 160W or more.

More importantly, you will notice that my text contains a lot of guesses. You will want to take out the guess work and get a good/great power monitoring system. I like the Victron BMV712 battery monitor. And the Victron series of MPPT solar controllers is really good too.

 

[PaulT]

A 50W panel is going to put out a rough max of 50/12 = 4 Amps or so, and charging happens about 8 hours a day, and at no more than 80% efficiency, because of dust, angle to the sun, etc. 8hrs*.8*4A = 25AH BEST CASE.

EM4,
Since a 12v panel typically puts out its watts at about 18 volts, 50/18

 

[PaulT]

I’ve tried three times to finish this post but it keeps being truncated.

Plan for less than full sun for fewer hours with the sun at a lower angle which reduces power collected.
50/18 volts <= 3 amps so more solar watts is a good idea.

Paul

 

[EM4]

I’ve tried three times to finish this post but it keeps being truncated.

Plan for less than full sun for fewer hours with the sun at a lower angle which reduces power collected.
50/18 volts <= 3 amps so more solar watts is a good idea.

Paul

Thanks very much Paul.

 

[EM4]

EM4,
Since a 12v panel typically puts out its watts at about 18 volts, 50/18

Thanks Vic, I'm starting to think at least 0ne more panel.

 

[EM4]

Generally, a good working solar system uses 2x the PV panels as the AH of the battery bank. Meaning you would need 218 Watts of solar. That rule of thumb also assumes you will be drawing the batteries down every night, which might not be true in your case.

The furnace is going to use the most power in your setup (no fridge?) and those use about 5A, and will be on (given Nevada/Arizona travel plans) no more than 6 hours per night... as a guess. That's 30 AH.

A 50W panel is going to put out a rough max of 50/12 = 4 Amps or so, and charging happens about 8 hours a day, and at no more than 80% efficiency, because of dust, angle to the sun, etc. 8hrs*.8*4A = 25AH BEST CASE.

Thus, you need more solar panel, for sure. I would look at 160W or more.

More importantly, you will notice that my text contains a lot of guesses. You will want to take out the guess work and get a good/great power monitoring system. I like the Victron BMV712 battery monitor. And the Victron series of MPPT solar controllers is really good too.

Hi there Vic, I like your reply ......thanks. Will have to digest that. Must add last week in Utah at 7000ft it was 34 degrees in the morning. The furnace must have run a total of 15 mins....in 3 different time frame....and then the heat of the sun took over... I leave the furnace off at night.....unless its going 5 degrees lower that freezing. Fridge runs on Propane.
Thanks very much

 

[jhickok]

I know this is an older topic, but maybe people will read this later to aid in their decision making.

Vic Harder seems to have provided excellent and accurate info here to aid in the decision, with the one caveat that he may have overestimated your needs. If money is no object, by all means, get another panel or two! However, the setup described is that you barely use your heater, have a water pump in a popup that probably doesn't get run THAT much, and use LED lights. Only other power draw is USB devices. Given that description, a 50W panel would totally be enough, because it's doubtful you will ever pull the max amps in a single day and run your battery down. Vic Harder assumed you drain your batteries down every night, and he stated that outright, so he was very helpful for the most power hungry scenario.

In the end, you may start running your laptop in the camper, using the heater more, or drawing more power somehow, so it's not bad to get more panels unless space, money, and time are an issue. Don't know how this worked out for you, but if you ended up with 100 watts, I bet you are doing more than fine as long as you have sun and haven't upped your power needs much.

 

[rubberlegs]

We opted for a Zamp 90W portable system for our 89Ah battery, which seems to work for our case at least in the CA/NV deserts. So instead of 2x the Ah, it's 1x. Major uses:

• 65L compression fridge (2 way)
• Heater fan not used much during sleep unless really cold, but definitely used in the evenings.
• iPad and phone charging
• LED lights
• Very occasional fan use
• Occasional water pump

However the panel doesn't do much of anything when it's cloudy. I don't think the voltage is high enough to help at all. Our winter trips in Washington State have been to state parks where... yup... we plug in to 110V.

 

[Vic Harder]

Vic Harder seems to have provided excellent and accurate info here to aid in the decision, with the one caveat that he may have overestimated your needs.

LOL. I am spec'ing out a new build, and boy ... I notice I tend to over-estimate... I hate running out!

 

[jhickok]

LOL. I am spec'ing out a new build, and boy ... I notice I tend to over-estimate... I hate running out!

If money can afford it, it's better safe than sorry!